This invention relates generally to ophthalmic surgery and, more specifically, to an adjustable suture and a method of wound closure that prevents unwanted induction of astigmatism.
Anterior segment ophthalmic surgical wound closure often has been associated with unwanted induction of astigmatism. In cataract implant surgery and in penetrating keratoplasty, the placement of radially orientated sutures is associated with a steepening of the curvature of the cornea in the meridian, corresponding to the suture, as shown in FIG. 1 and as will be described below. This steepening of the curvature results in an astigmatic refractive error with the positive cylinder axis orientated along the steep meridian. In order to secure the wound and to avoid leakage of aqueous humor, the surgeon generally ties the suture very tight. If the suture is tied too loose, there can be a flattening of the cornea and leakage of aqueous humor. Furthermore, there can be a flattening of the cornea absent leakage due to shifting of the wound approximations. This flattening of the cornea, with or without leakage, also can lead to astigmatic refractive error with the positive cylinder axis orientated 90.degree. to the meridian of the wound.
Efforts have been made to avoid unwanted astigmatic changes. For example, surgical techniques have been developed that create as small a wound, i.e. short arc of incision) as possible. This type of short arc incision is used in cataract implant surgery. In penetrating keratoplasty, the use of a continuous or running suture with post-operative adjustment of suture tension has been suggested to reduce astigmatism. None of these procedures has proved to be totally satisfactory in preventing post-surgical astigmatism.
As suggested above, post-operative adjustment of suture tension may reduce astigmatism. Therefore, it may be possible to adjust the focal point of the eye by the appropriate adjustment of a suture. Generally, nylon or cat-gut sutures are used to close the surgical wound. For the most part, surgical sutures can be loosened or tightened by untying the knot, drawing the suture tighter, and then retying the knot. In some situations, the suture must be snipped and retied or the suture must be removed and replaced. In delicate surgeries, for example ophthalmological surgery, it is quite difficult to adjust the tension on a suture once it is in place. The sutures placed in the eye are particularly fine. Adjusting the tension on the suture by conventional methods is painstaking and time consuming and can result in discomfort and inconvenience for the patient.